1. Field of the Invention
The present invention relates to construction equipment which drives a working device such as a boom or the like in accordance with a manipulation of an electric control lever, and more particularly, to construction equipment having an electric control lever, which can intercept a control signal that is applied to a flow control valve when trouble occurs in the electric control lever or a control unit (ECU).
2. Description of the Prior Art
As illustrated in FIG. 1, construction equipment having an electric control lever in the related art includes an engine 50; a variable-displacement hydraulic pump (hereinafter referred to as a “hydraulic pump”) 51 and a pilot pump 52 which are driven by the engine 50; a hydraulic actuator 53 such as a hydraulic cylinder or the like which is operated by the hydraulic pump 51; an electronic flow control valve (hereinafter referred to as a “flow control valve”) (MCV) 54 installed in a flow path between the hydraulic pump 51 and the hydraulic actuator 53 to be shifted to control a start, a stop, and a direction change of the hydraulic actuator 53; an electronic control lever (hereinafter referred to as a “control lever”) 56 outputting a manipulation signal in proportion to a manipulation amount; electro-proportional valves 57 and 58 converting hydraulic fluid from the pilot pump 52 into a secondary signal pressure in accordance with a current value applied from the control unit (ECU) 55 in proportion to the manipulation signal of the control lever 56, and shifting a spool of the flow control valve 54 in accordance with the converted signal pressure; a manipulation locking lever (hereinafter referred to as a “locking lever”) 59 outputting a manipulation signal for control in preference to the manipulation signal of the control lever 56 when an error occurs in the manipulation signal of the control lever 56; and a solenoid valve 60 installed in a discharge flow path of the pilot pump 52 and shifted when the locking lever 59 is manipulated to intercept the signal pressure applied from the pilot pump 52 to the electro-proportional valves 57 and 58.
If the manipulation signal is input from the control lever 56 to the control unit 55 and the locking lever 59 is released from a locking position, the manipulation signal of the control lever 56 is calculated by a predefined algorithm, and is input to the electro-proportional valves 57 and 58 as a control signal.
By contrast, if the manipulation signal is input from the control lever 56 to the control unit 55 and the locking lever 56 is shifted to a locking position, the manipulation signal from the control lever 56 is disregarded even if the manipulation signal is input to the control unit 55.
At the same time, the discharge flow path of the pilot pump 52 can be opened or closed by a switch 61 installed on the locking lever 59. That is, if the locking lever 59 is shifted to a locking position, the solenoid valve 60 is kept in a closed state (e.g. a state as illustrated in FIG. 1), and thus hydraulic fluid supplied from the pilot pump 52 to the electro-proportional valves 57 and 58 can be intercepted.
On the other hand, in a hydraulic system using self pilot operated electro-hydraulic proportional values as illustrated in FIG. 5, the opening and closing of the electro-hydraulic proportional valves P1 to P4 and P5 to P8 is controlled by hydraulic fluid of hydraulic actuators 4 and 4b in accordance with a manipulation signal from a control lever 7. Accordingly, malfunction of working devices such as a boom or the like due to an erroneous manipulation signal of the control lever 7 or an error of the control unit cannot be cleared up.
In a hydraulic system having an electric control lever, electronic hydraulic control valves driven by the manipulation of the electric control lever, and the like, which is disclosed in U.S. Pat. No. 4,881,450, a sensor switch that can sense the non-manipulation state (i.e. neutral state) of the control lever is installed in order to prevent the malfunction of a working device. That is, when the control lever is in a neutral state, a drive signal from a controller to the hydraulic control valves is cut off.
In the hydraulic system of U.S. Pat. No. 4,881,450 as described above, in the case of operating a preferable control signal of the electronic proportional valves against the manipulation signal of the electric control lever, conversion logic according to a control signal delay, filtering, or forward/reverse conversion is frequently used for smooth acceleration/reduction or direction change of the working device. In this case, the driving current of the electronic proportional valves is voluntarily short-circuited by the sensor switch installed on the control lever, and thus it is difficult to apply a control signal that is processed by software thereto.